Transgenic plants having transformed plastid genomes and progeny thereof

ABSTRACT

Plants having transformed plastid genomes comprising a construct comprising attL and attR sites and a gene of interest, where the plants comprise an integrase and, optionally a selectable marker gene, and methods of making the plants.

This application is a §371 application of PCT/US02/09537 filed Mar. 29, 2002, which in turn claims priority to U.S. Provisional Application 60/279,615 filed Mar. 29, 2001. The entire disclosure of each of the above-identified applications is incorporated herein by reference.

FIELD OF THE INVENTION

This invention is related to the fields of molecular biology and transgenic plants. More specifically, the present invention provides compositions and methods which facilitate the insertion and excision of transgenes from the plastids of higher plants.

BACKGROUND OF THE INVENTION

Several publications and patent documents are referenced in this application by numerals in parentheses in order to more fully describe the state of the art to which this invention pertains. The disclosure of each of these publications and patent documents is incorporated by reference herein.

The plastid genome of higher plants is a circular double-stranded DNA molecule, 120-160 kb in size, which may be present in 1900-50000 copies per leaf cell, which carries about 100 chloroplasts (Bendich 1987; Sugiura 1992). There are several reasons why incorporation of transgenes in the plastid genome may be preferred over incorporation of transgenes into the nuclear genome. The advantages of plastid transformation include: natural containment due to lack of pollen transmission in most crops; high-level protein expression; feasibility of expressing multiple genes from operons; and lack of position effect (Maliga 1993; Maliga et al. 1993; Heifetz 2000; Bock 2001; Heifetz and Tuttle 2001; Maliga 2002). Useful traits expressed in chloroplasts are the Bacillus thuringiensis insecticidal protein (McBride et al. 1995; Kota et al. 1999), herbicide resistance (Daniell et al. 1998; Lutz et al. 2001; Ye et al. 2001) and expression of human somatotropin (Staub et al. 2000).

For almost a decade, plastid transformation was feasible only in tobacco (Nicotiana tabacum). Plastid transformation has recently been extended to Arabidopsis thaliana (Sikdar et al. 1998), potato (Solanum tuberosum) (Sidorov et al. 1999), tomato (Ruf et al. 2001) and progress has been made towards transforming plastids in rice (Khan and Maliga 1999). Plastid transformation in these new species has been very inefficient as compared to tobacco. Clearly, a need exists for improved compositions and methods for expressing transgenes in the plastids of a wider range of higher plant species.

SUMMARY OF THE INVENTION

In accordance with the present invention compositions and methods are provided for catalyzing insertion of heterologous nucleic acid sequences into the genome of higher plants. One exemplary method comprises i) providing a recipient plant having a transformed plastid genome which contains a first recombination site; ii) introducing an integrase into the recipient plant and further introducing a heterologous DNA construct comprising a second recombination site, a sequence encoding a gene of interest and optionally a selectable marker gene into the plant, wherein the integrase acts on the first and second recombination sites and catalyzes the insertion of the sequence encoding the gene of interest into the plastid genome.

In a preferred embodiment, the first and second recombination sites are interchangeably referred to as attB and attP sites and the integrase is a phiC31 integrase.

The integrase may be stably or transiently expressed in the target plant. Methods and compositions for effecting stable or transient expression are provided herein.

In accordance with the present invention, endogenous recombination sites within the plastid genome have been discovered. Accordingly, a further method of the invention comprises catalyzing insertion of heterologous nucleic acid sequences encoding a gene of interest utilizing an integrase that acts on at least one endogenous recombination site.

In certain embodiments, selectable marker genes are utilized to identify transformed plants. In cases where it is desirable to excise such selectable marker genes, the methods of the invention encompass the use of the CRE-LOX system to eliminate sequences from the transgenic plants of the invention.

In yet another aspect, plasmids are provided with facilitate practicing the methods of the present invention.

Also encompassed within the scope of the invention are plants and progeny plants transformed using the methods disclosed.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematic of transformation of the plastid genome which is formed by two recombination events via homologous targeting sequences. Plastid genome segments included in vector are marked as left and right targeting regions (LTR, RTR), respectively.

FIG. 2 is a map of plastid transformation vector pSAC114. The vector backbone is pPRV1 (Zoubenko et al. 1994). The (ScaI/KpnI) to (ScaI/SacI) fragment is Seq. ID No. 4. Positions of the plastid genes rrn16, trnV, rps12/7, the aadA gene (flanked by direct lox sites), the attB sequence (Seq. ID No. 3) and the relevant restriction sites are marked.

FIG. 3 is the map of the int gene in transient expression plasmid pKO107. SacI-HindIII fragment is Seq. ID No. 25. The int coding region and positions of the relevant restriction sites are marked.

FIG. 4 is the map of the int gene in transient expression vector pKO111. The SacI to HindIII fragment is Seq. ID No. 26. The integrase gene, the deltaF/deltaL psbL editing fragment (Chaudhuri and Maliga 1996) and positions of the relevant restriction sites are marked.

FIG. 5 is a map of the episomally maintained transient int expression vector pKO126. The plastid ori (pt-ori) sequence (Staub and Maliga 1994a), aadA gene, int gene (coding region is Seq. ID No. 5) and the relevant restriction sites are marked.

FIG. 6 is a linearized map of donor vector pKO103 (Seq. ID No. 7). A circular representation is shown in FIG. 9A. The attP sequence (Seq. ID No. 6), neo gene, lox site (Seq. ID No. 2) and relevant restriction sites are marked.

FIG. 7 shows maps of (A) the wt and (B) pSAC114 transformed plastid genomes and (C) a DNA gel blot to confirm plastid DNA structure. Total cellular DNA was digested with the BamHI restriction endonuclease and probed with the wild-type EcoRI-EcoRV plastid DNA fragment (heavy line). The size of hybridizing fragments is marked in the wt and Nt-pSAC114 maps. The Nt-pSAC114.2A DNA sample is homoplasmic for the transformed plastid genome structure, while Nt-pSAC114.2B still has some wt plastid genome copies present. Positions of the plastid genes rrn16, trnV, rps12/7, the aadA gene (flanked by direct lox sites), the attB sequence and the relevant restriction sites are marked.

FIG. 8 shows (A) a partial map of the Nt-pSAC114 plastid genome (B), Nt-pSAC114 plastid genome after excision of aadA by CRE, (C) a DNA gel blot to confirm plastid DNA structure after aadA excision. Excision of aadA in the Nt-pSAC114 plastid genome was triggered by transformation with Agrobacterium carrying cre plasmids pKO30 (TP22) or pKO31 (TP5). Total cellular DNA was digested with the BamHI restriction endonuclease and probed with plastid DNA (EcoRI-EcoRV) and aadA (NcoI-XbaI) fragments. Fragments hybridizing with the ptDNA probe are marked in FIG. 7; those with aadA in this Fig. Note absence of aadA in CRE-transformed plants. Position of plastid genes rrn16, trnV, rps12/7, the aadA gene, lox sites, attB sequence and the relevant restriction sites are marked.

FIG. 9 is the schematic experimental design for integration of the neo gene mediated by transient expression of INT in plastids. Shown are (A) The transformed plastid genome containing the aadA gene flanked by two directly oriented lox sites and an attB site (the KpnI-SacI sequence derives from pSAC113, Seq. ID No.4); the donor vector pKO103, carrying an attP site, a neo gene and one lox site (Seq. ID No. 7), and a plasmid for transient expression of INT (coding region Seq. ID No.5) (pKO107, pKO111, or pKO126). (B) The plastid genome obtained after INT mediated insertion of the neo gene and a lox site. attL and attR sequences were generated by INT mediated attB-attP recombination.

FIG. 10 shows (A) a partial map of the Nt-pSAC114 plastid genome after integration of donor vector pKO103. INT function was provided transiently by plasmids pKO107 or pKO111. PCR primer positions and the predicted size of junction fragments are shown. Plastid genes rrn16, trnV, rps12/7, aadA (flanked by direct lox sites), the attL sequence, the neo gene, a third lox site, an attR sequence and the relevant restriction sites are marked. (B) PCR amplification of attL and attR junctions.

FIG. 11 shows (A) the components for INT-mediated integration of the pK0103 donor vector into the Nt-pSAC114 plastid genome. Transient INT function is provided by plasmids pK0170 or pKO111. (B) The aligned attB and attP sequences. The attB sequence corresponds to nucleotides 9-58 of SEQ ID NO: 3 and the attP sequence corresponds to nucleotides 137-186 of SEQ ID NO: 6. (C) The attL and attR sequences formed by INT-mediated recombination of attB and attP sequences. The attL sequence corresponds to nucleotides 5-54 of SEQ ID NO: 8 and the attR sequence corresponds to nucleotides 134-183 of SEQ ID NO: 9. (D) The product of INT-mediated integration of the pK0103 donor vector in the Nt-pSAC114 plastid genome. Plastid genes rrn16, trnV, rps12/7, the aadA gene (flanked by direct lox sites), the attB sequence, the attR sequence, the neo gene, the attL sequence, an attR sequence, a third lox site and the relevant restriction sites are marked.

FIG. 12 is a schematic design for integration of foreign DNA mediated by transient expression of INT in plastids. Shown are (A) the plastid genome containing a marker gene (mg) flanked by two directly oriented lox sites (Seq. ID No. 1) and an attB site (Seq. ID No. 3). (B) The recipient plastid genome containing one lox site and an attB site after CRE mediated deletion of the marker gene. (C) The donor vector carrying an attP site (Seq. ID No. 6), ColE1 ori, a marker gene (mg), one lox site and a gene of interest (goi) and the int plasmid for transient expression of INT. (D) The plastid genome after INT mediated insertion of the donor vector. attL and attR sequences (Seq. ID No. 8 and Seq. ID No. 9 respectively) were generated by INT mediated attB-attP recombination. (E) The plastid genome after CRE mediated excision of attL and the marker gene.

FIG. 13 is a schematic design of System 2A for integration of foreign DNA mediated by a plastid encoded INT. Shown are (A) the plastid genome containing a promoter (P1), RBS, an aadA coding region flanked by two directly oriented lox sites, RBS, an int coding region, a terminator (T1) and an attB site. This plasmid is the progenitor of recipient plastid genome. (B) The recipient plastid genome after CRE excision. It contains only P1, one lox site, a RBS and an int coding region, a terminator (T1) and an attB site.(C) The donor vector carrying an attP site, a marker gene (mg), ColiE1 ori, one lox site, a RBS, coding region of the gene of interest (goi) and terminator (T3). (D) The plastid genome after INT mediated insertion of the donor vector. attL and attR were generated by INT mediated attB-attP recombination. (E) The plastid genome after CRE mediated deletion of the int gene, attL and the marker (mg) gene.

FIG. 14 is an experimental design of System 2B for integration of foreign DNA mediated by expressing a plastid encoded INT from a dicistronic operon. Shown are (A) the plastid genome containing one lox site, a dicistronic int-aadA gene including a promoter (P1), editing segment (Ed), int coding region, RBS, aadA coding region and terminator (T1). (B) The donor vector carries an attP site, a neo gene, ColE1 ori, lox site and a gene of interest (goi). (C) The plastid genome after integrase mediated insertion of donor vector. attL and attR sequences were generated by INT mediated attB-attP recombination. (D) The plastid genome after CRE mediated deletion of the chimeric int-aadA gene, the attL site and the neo gene.

FIG. 15 is a schematic design for integration of foreign DNA mediated by nuclear encoded plastid targeted INT. Shown are (A) the recipient plastid genome containing one lox site and an attB site. INT is expressed from a nuclear gene. (B) The donor vector carrying an attP site, ColE1 ori, a marker gene, one lox site and a gene of interest (goi). (C) Plastid genome obtained after INT mediated insertion of donor vector. attL and attR sequences were generated by INT mediated attB-attP recombination. (D) The plastid genome after CRE mediated excision of attL, the ColE1 ori and the marker gene.

FIG. 16 shows the map of the T-DNA region in Agrobacterium binary vector pKO117. The Agrobacterium binary vector has the pPZP222 backbone (Hajdukiewicz et al. 1994) and is a pKO30 derivative as described in WO 01/21768. The int gene sequence (EcoRI-PstI) is Seq. ID No. 27. Positions of left and right borders (LB and RB), the gentamycin resistance gene (aacC1), nopaline syntase untranslated 3′ end (Tnos), int coding region, transit peptide fragment (TP22), 2′ Agrobacterium promoter (P2′) and the relevant restriction sites are marked.

FIG. 17 is a schematic design for INT mediated integration of bar in the plastid genome. Shown are (A) the recipient plastid genome containing a lox site and an attB site. INT is provided transiently from a plastid or nuclear gene. (B) The donor vector carries an attP site, ColE1 ori, a marker gene (P1, T1), one lox site and a bar gene (P2, T2). Suitable bar genes are described in (Lutz et al. 2001). (C) The plastid genome after INT mediated insertion of donor vector. attL and attR sequences were generated by INT mediated attB-attP recombination. (D) The plastid genome after CRE mediated excision of attL and the marker gene.

FIG. 18 is a schematic design for INT mediated integration of bar. Shown are (A) the plastid genome containing a P1 promoter, a lox site, a RBS and a marker coding region with a T1 terminator, a second lox site in direct orientation with the first lox site and an attB site. This plastid genome is the progenitor of the recipient line. (B) The recipient plastid genome obtained by excision of the marker gene (mg) by CRE. (C) Donor vector with dicistronic bar operon has an attP site, ColE1 ori, P2 promoter, a marker coding region, one lox site, a RBS and a bar coding region with a T1 terminator.(D) Donor vector with promoter-less dicistronic bar operon consists of an attP site, ColE1 ori, RBS, a marker coding region, lox site, RBS, and a bar coding region with a T1 terminator. (E) The plastid genome after INT mediated insertion of donor vector with dicistronic bar operon (FIG. 18C above). attL and attR sequences were generated by INT mediated attB-attP recombination. (F) The plastid genome after INT mediated insertion of donor vector with promoter-less dicistronic bar operon shown in FIG. 18D. attL and attR sequences were generated by INT mediated attB-attP recombination. (G) The plastid genome after CRE mediated excision of the attL and marker gene sequences from the plastid genomes shown in FIG. 18E and FIG. 18F.

FIG. 19 is a schematic design for marker gene excision by a transiently expressed CRE. Shown are (A) the recipient plastid genome with lox and attB sites. INT is provided transiently from a plastid or nuclear gene. (B) Donor vector with attP, ColE1 ori, a P1:aadA:codA:T1 fusion, a lox site, and a goi. (C) The plastid genome obtained after INT mediated insertion of donor vector. (D) The plastid genome after transient CRE mediated excision of the attL sequence and the fused (aadA:codA) marker gene.

DETAILED DESCRIPTION OF THE INVENTION

The following definitions are provided to facilitate an understanding of the present invention.

Heteroplastomic refers to the presence of a mixed population of different plastid genomes within a single plastid or in a population of plastids contained in plant cells or tissues.

Homoplastomic refers to a pure population of plastid genomes, either within a plastid or within a population contained in plant cells and tissues. Homoplastomic plastids, cells or tissues are genetically stable because they contain only one type of plastid genome. Hence, they remain homoplastomic even after the selection pressure has been removed, and selfed progeny are also homoplastomic. For purposes of the present invention, heteroplastomic populations of genomes that are functionally homoplastomic (i.e., contain only minor populations of wild-type DNA or transformed genomes with sequence variations) may be referred to herein as “functionally homoplastomic” or “substantially homoplastomic.” These types of cells or tissues can be readily purified to a homoplastomic state by continued selection.

Plastome refers to the genome of a plastid.

Transplastome refers to a transformed plastid genome.

Transformation of plastids refers to the stable integration of transforming DNA into the plastid genome that is transmitted to the seed progeny of plants containing the transformed plastids.

Selectable marker gene refers to a gene or a nucleic acid sequence that upon expression confers a phenotype by which successfully transformed plastids or cells or tissues carrying the transformed plastid can be identified. One class of exemplary selectable marker genes comprises antibiotic or herbicide resistance genes. Another class of marker does not confer resistance but enables visual screening of transformed plant cells. Such markers include, without limitation, green fluorescent proteins.

Transforming DNA refers to homologous DNA, or a heterologous DNA flanked by homologous DNA, which when introduced into plastids becomes part of the plastid genome by homologous recombination. In this type of transformation, a sufficient degree of homology between the homologous tranforming DNA and the targeted plastid genome is all that is required for insertion of the transforming DNA into the plastid genome.

An alternative type of transforming DNA refers to a DNA which contains recombination site sequences for a site-specific recombinase or integrase. Insertion of this type of DNA is not dependent of the degree of homology between the transforming DNA and the plastid to be transformed but rather is catalyzed by the action of the recombinase or integrase on the first and second recombination sites.

Recombination sites as used herein refers to specific polynucleotide sequences that are recognized by the recombinase or integrase enzymes described herein. Typically, two different sites are involved, one present in the target nucleic acid and another on the nucleic acid that is to be integrated at the target recombination site. The terms attB and attP attachment sites originally from a bacterial target and a phage donor, respectively, are used herein although recombination sites for particular enzymes may have different names.

Operably linked refers to two different regions or two separate genes spliced together in a construct such that both regions will function to promote gene expression and/or protein translation.

“Nucleic acid” or a “nucleic acid molecule” as used herein refers to any DNA or RNA molecule, either single or double stranded and, if single stranded, the molecule of its complementary sequence in either linear or circular form. In discussing nucleic acid molecules, a sequence or structure of a particular nucleic acid molecule may be described herein according to the normal convention of providing the sequence in the 5′ to 3′ direction. With reference to nucleic acids of the invention, the term “isolated nucleic acid” is sometimes used. This term, when applied to DNA, refers to a DNA molecule that is separated from sequences with which it is immediately contiguous in the naturally occurring genome of the organism in which it originated. For example, an “isolated nucleic acid” may comprise a DNA molecule inserted into a vector, such as a plasmid or virus vector, or integrated into the genomic DNA of a prokaryotic or eukaryotic cell or host organism.

When applied to RNA, the term “isolated nucleic acid” refers primarily to an RNA molecule encoded by an isolated DNA molecule as defined above. Alternatively, the term may refer to an RNA molecule that has been sufficiently separated from other nucleic acids with which it would be associated in its natural state (i.e., in cells or tissues). An isolated nucleic acid (either DNA or RNA) may further represent a molecule produced directly by biological or synthetic means and separated from other components present during its production.

The terms “percent similarity”, “percent identity” and “percent homology” when referring to a particular sequence are used as set forth in the University of Wisconsin GCG software program.

The term “functional” as used herein implies that the nucleic or amino acid sequence is functional for the recited assay or purpose.

The phrase “consisting essentially of” when referring to a particular nucleotide or amino acid means a sequence having the properties of a given SEQ ID NO:. For example, when used in reference to an amino acid sequence, the phrase includes the sequence per se and molecular modifications that would not affect the basic and novel characteristics of the sequence.

A “replicon” is any genetic element, for example, a plasmid, cosmid, bacmid, phage or virus, that is capable of replication largely under its own control. A replicon may be either RNA or DNA and may be single or double stranded.

A “vector” is a replicon, such as a plasmid, cosmid, bacmid, phage or virus, to which another genetic sequence or element (either DNA or RNA) may be attached so as to bring about the replication of the attached sequence or element.

An “expression operon” refers to a nucleic acid segment that may possess transcriptional and translational control sequences, such as promoters, enhancers, translational start signals (e.g., ATG or AUG codons), polyadenylation signals, terminators, and the like, and which facilitate the expression of a polypeptide coding sequence in a host cell or organism.

The term “oligonucleotide,” as used herein refers to primers and probes of the present invention, and is defined as a nucleic acid molecule comprised of two or more ribo- or deoxyribonucleotides, preferably more than three. The exact size of the oligonucleotide will depend on various factors and on the particular application and use of the oligonucleotide.

The terms “transform”, “transfect”, “transduce”, shall refer to any method or means by which a nucleic acid is introduced into a cell or host organism and may be used interchangeably to convey the same meaning. Such methods include, but are not limited to, transfection, electroporation, microinjection, PEG-fusion, biolistic bombardment and the like.

A “clone” or “clonal cell population” is a population of cells derived from a single cell or common ancestor by mitosis.

A “cell line” is a clone of a primary cell or cell population that is capable of stable growth in vitro for many generations.

Stable transformation of the tobacco plastid genome is achieved in tobacco leaves using the biolistic method for DNA delivery. The foreign heterologous DNA integrates into the plastid genome by homologous recombination via the left and right targeting regions of the plastid transformation vector (FIG. 1). The targeting regions are derived from the plastid genome. The insertion site is selected so that the transgene does not interfere with the expression of the flanking plastid genes. The heterologous DNA segment typically contains a selectable marker gene and a gene of interest (goi) with no selectable phenotype. Expression of the antibiotic resistance gene confers a selective advantage to the chloroplast, which gradually replaces the plastids lacking the antibiotic resistance gene. The homoplastomic state is obtained when all the plastid genome (plastome) copies are transformed, which takes about 20 cell generations (Moll et al. 1990). The sorting out process takes place while the leaf segment is cultured on an antibiotic containing shoot regeneration medium. The shoots regenerated on the selective medium are typically chimeric, containing sectors with transformed and wild type plastid genome copies. Genetically stable, homoplastomic plants are obtained by shoot regeneration from transformed leaf sectors. In an exemplary protocol, leaf tissue is targeted for biolistic DNA delivery of heterologous DNA comprising homologous DNA recombining segments and nucleic acid sequences encoding spectinomycin resistance as a selective marker. In an alternative embodiment of this method, spectinomycin resistance conferred by insertion of sequences encoding a mutant plastid 16S ribosomal RNA gene (Svab et al. 1990; Staub and Maliga 1993). In yet another embodiment, spectinomycin resistance was conferred by the more efficient bacterial aadA gene (Svab and Maliga 1993). Streptomycin resistance was carried by both vector systems, but spectinomycin resistance was used as a primary means of selection. The pPRV (plastid repeat vector) plasmids are a plastid vector series with convenient restriction sites at the insertion site with no significant read-through transcription (Zoubenko et al. 1994). A variant of this plastid transformation method was reported from three European laboratories which utilize PEG treatment of protoplasts as a method of DNA introduction (Golds et al. 1993; O'Neill et al. 1993; Koop et al. 1996).

An alternative approach to plastid transformation has been attempted by Dr. Henry Daniell and colleagues who built a vector system designed to function as an independent replicon and utilized chloramphenicol resistance as a selectable marker (Daniell 1993). No stable maintenance of these vectors in chloroplasts or selection of plastid transformation events by chloramphenicol resistance was reported.

Perceiving DNA delivery as the bottleneck of plastid transformation, a sophisticated chloroplast microinjection protocol has recently been developed. Thus far the system has been used only to demonstrate transient expression of the microinjected DNA (Knoblauch et al. 1999).

It appears that there are two issues of importance for general applicability of plastid transformation.

1) Choice and expression level of selectable marker genes. The protocols for non-tobacco species have utilized aadA as the selectable marker encoding aminoglycoside 3″-adenyltransferase and selection for resistance to spectinomycin (potato, tomato, Arabidopsis) or streptomycin (rice) which are rendered inactive by adenylation. Both spectinomycin and streptomycin inhibit protein synthesis on prokaryotic-type ribosomes. Interestingly, most other inhibitors of protein synthesis on prokaryotic-type ribosomes (for example gentamycin, hygromycin) have been shown to be unsuitable for selection of plastid transformation events, although they make the cells resistant once the antibiotic inactivating gene is present in all plastid genome copies. The same is true for the bar gene that confers PPT resistance when present in all plastid genome copies, but is not suitable for direct selection of transplastomic clones (Lutz et al. 2001). This observation suggested that increasing the output of gene product per marker gene copy should improve the performance of the marker genes. Indeed, kanamycin resistance, which in the past was considered to be an inefficient marker (Carrer et al. 1993) was improved 10-fold by expressing the neo gene at a higher level. The efficiency of selection with the new kanamycin-resistance (neo) genes and the spectinomycin resistance (aadA) genes is now comparable. Also, we attribute successful plastid transformation in rice to high-level expression of the aadA gene (Khan and Maliga 1999). High level expression may be important during the early stage of plastid transformation when only a few of the thousands of genome copies are transformed. However, accumulation of the marker gene product at 10% to 20% of total soluble protein is unacceptable when all the genome copies are carrying the selectable marker gene (Kuroda and Maliga 2001b; Kuroda and Maliga 2001a). Removal of selectable marker genes by loop-out via directly repeated sequences has been shown (Iamtham and Day 2000). However, this is a complicated system that is difficult to control. We have utilized the CRE/lox site-specific recombination system for efficient elimination of the selectable marker genes (Corneille et al. 2001; Hajdukiewicz et al. 2001).

2) Competence of plastids to integrate foreign DNA. The number of plastid genome copies in the leaves of different species is comparable. However, plastid transformation efficiencies are species dependent. Plastid transformation efficiency in bombarded potato and Arabidopsis leaf cultures was 10-fold and 100-fold lower than in tobacco, respectively (Sikdar et al. 1998; Sidorov et al. 1999). Since the chloroplast size and genome copy number, at least in potato, is about the same as in tobacco, we assume, that the difference in the transformation efficiency is due to differences in the efficiency with which foreign DNA is incorporated into the plastid genome. It is not known how to activate the recombination system of plastids to enhance transformation competence. In accordance with the present invention, methods and compositions employing the phiC31 integrase are provided which enhance the efficiency of plastid transformation in a wider range of plant species.

Site-specific Phage Recombinases for Excision and Integration of Foreign DNA

Methods employing two different bacteriophage recombinases for the excision and integration of foreign DNA into the plastid genome of higher plants are described herein. Several prokaryotic and lower eukaryotic site-specific recombination systems have been shown to operate successfully in higher eukaryotes. In yeast, plant and animal cells functional site-specific recombination systems have been described from bacteriophages P1 (CRE-loxP) (see below) and Mu (Gin-gix), and from the inversion plasmids of Saccharomyces cerevisiae (FLP-frt) (Morris et al. 1991; Lyznik et al. 1996) and Zygosaccharomyces rouxii (R-RS) (Onouchi et al. 1991; Onouchi et al. 1995). In each of these systems, no additional factor aside from the recombinase and target sequences is required for recombination.

The CRE-loxP site-specific recombination system of bacteriophage P1 has been studied extensively in vitro and in E. coli (Craig 1988; Adams et al. 1992; Guo et al. 1997). Expression of the CRE protein (38.5 kDa) is sufficient to cause recombination between 34 bp loxP sites that consist of 13 bp inverted repeats separated by 8 bp asymmetric spacer sequence. If there are two loxP sites within a DNA segment, the result of the recombination reaction depends on the relative position of the recombination sites. If the recombination sites form a direct repeat, that is they are in the same orientation, recombination results in deletion of the intervening DNA. If the recombination sites are in an inverted orientation, CRE-mediated recombination results in an inversion of the intervening DNA. In site-specific DNA integration, recombination between a site on a circular molecule and a site on the chromosome results in the insertion of the circular molecule into the chromosome. However, after integration, the DNA is flanked by two lox sites in the same orientation and therefore can be excised if the recombinase is present. There are many applications for the site-specific recombination systems to study gene function and development. The CRE-loxP system has been explored in higher plants to facilitate intra- and inter-molecular site-specific recombination, removal of selectable marker genes and for site-specific insertion of foreign DNA in the nucleus (Dale and Ow 1990; Odell et al. 1990; van Haaren and Ow 1993; Gleave et al. 1999; Choi et al. 2000; Day et al. 2000). Application of the CRE-lox site-specific recombination system for the removal of marker genes has been reviewed recently (Ow 2001). The CRE-lox site-specific recombination system has been also employed for the removal of selectable marker genes from the plastid genome(Corneille et al. 2001; Hajdukiewicz et al. 2001).

The CRE-lox system is reversible, mediating both excision and integration of sequences flanked by lox sites, with ˜100-fold bias in favor of excision. Thus, a better choice for integration is the phage phiC31 integrase (INT) which catalyses integration between non-identical attB and attP sequences (bacterial and phage attachment regions, respectively), and cannot mediate excision without additional factors (Thorpe and Smith 1998). The Streptomyces phiC31 integrase catalyses unidirectional integration in its host (Thorpe et al. 2000), and has been successfully utilized for efficient, unidirectional integration of foreign DNA in mammalian cells (Groth et al. 2000; Thyagarajan 2001) and yeast (Thomason et al. 2001). There are three elements of the system: (1) a target site in the genome (attB); (2) a vector with an attP site and (3) integrase (INT) enzyme. The location of the attB and attP are interchangeable: if attP is located in the genome, attB is present in the vector. Minimal sequences required for attB and attP function in vitro were defined to be 34 bp and 39 bp, respectively (Groth et al. 2000). The three bp core, TTG, within which recombination takes place, is shared by attB and attP. There is little sequence similarity outside the core: including the core, only 15 nucleotides are conserved between the minimal attB (34 bp) and attP (39 bp) sequences. The consequence of the lack of sequence similarity between attB and attP is that the recombination products, attL (left junction) and attR (right junction)are very different from the parental sites, and therefore are not recognized by the integrase. In mammalian cells, longer sequences were found to be more efficient (Groth et al. 2000). We describe here the use of phiC31 site-specific recombinase for the insertion of foreign DNA into the plastid genome. Full size 55-bp attB and 217-bp attP regions were utilized in the following experiments.

Alternative Methods for Introducing INT Activity in Higher Plants to Facilitate Transgene Integration

The source of INT can be a DNA or RNA template, or purified INT protein may be provided directly. DNA templates encoding INT, may be provided transiently, without stable integration into the plastid or nuclear genomes. In an alternative approach the INT encoding sequence may be expressed in a stable fashion by incorporating the integrase gene into one of the plant's genomes. mRNA sequences encoding INT or the purified INT protein provide a transient, rather than a stable source of INT as both are degraded in the cell over time.

Using a DNA template as the source of INT is compatible with both transient and stable expression of the enzyme. Transient supply of INT in plastids could be ensured by incorporating an INT coding region in a cassette with plastid signals in a Bluescript (or similar bacterial) plasmid. The Bluescript plasmid replicates in E. coli, but not in plastids, resulting in rapid elimination of the int gene. If higher levels of INT are needed, and presence of INT over a longer period of time is desirable, the int gene can be incorporated in a shuttle plasmid which is episomally maintained. Shuttle plasmids, such as the NICE plasmid (Staub and Maliga 1994a), are maintained in the absence of any selection for a period of time, but are unstable and eventually lost. To limit the expression of INT to plastids, the N-terminus could be translationally fused with a DNA segment encoding an edited C nucleotide. An exemplary DNA fragment for this purpose is the 22 nucleotide psbL editing segment (Chaudhuri and Maliga 1996) from which translation depends on creating an AUG initiation codon from the ACG codon by RNA editing which is specific to plastids. INT may be transiently expressed from a nuclear gene that is not integrated into the nuclear genome, which encodes an N-terminal extension to target the protein to plastids. Vectors based on plant viruses can also be beneficially employed for transient expression of INT, for example tobacco mosaic virus (TMV) (Kumagai et al. 1995; Kumagai et al. 2000), potato virus X (Rommens et al. 1995), tobacco rattle virus (Ratcliff et al. 2001), gemini viruses (Kanevski et al. 1992; Peele et al. 2001) or by an Agrobacterium transient gene expression system (Grimsley et al. 1989).

Alternatively, INT activity is provided from a stably integrated gene. The gene may be expressed in the plastid genome from plastid expression signals with or without an RNA editing segment. Alternatively, INT may be expressed from a nuclear gene, and provided with an N-terminal extension to target INT from the cytoplasm to plastids. The nuclear INT may also be expressed from a regulated promoter (Aoyama and Chua 1997; Martinez et al. 1999; Zuo and Chua 2000; Zuo et al. 2000).

As mentioned above, transient integrase activity in plastids may also be accomplished by introducing mRNA rather than DNA as template to produce the integrase enzyme. Using mRNA as the source of integrase has the advantage of supplying enzymatically active integrase for a brief period, but avoids the need to remove the integrase from the plastid or nuclear genomes. A transient supply of INT can also be provided by injecting the purified protein into the plant cell cytoplasm (with plastid-targeting sequence) or microinjected directly into plastids.

Methods for transient gene expression utilizing PEG, electroporation, microinjection, or biolistic transformation have been described (Maliga et al. 1995; Potrykus and Spangenberg 1995; Gelvin and Schilperoort 1997).

The following examples are provided to facilitate the practice of the present invention. They are not intended to limit the invention in any way.

EXAMPLE 1 Transient INT Expression in Plastids for Site-specific Integration of Foreign DNA

There are three components of the transient INT system: 1) a transplastomic recipient line carrying an attB sequence 2) an INT encoding vector for transient expression in plastids and 3) a donor vector for integration which contains an attP sequence, a marker gene and a gene of interest (goi).

The following materials and methods are provided to facilitate the practice of Example 1.

Plastid Vector for the Introduction of an attB Sequence into the Plastid Genome

A plastid transformation vector has been designed that contains an attB sequence and an addA gene that is flanked by two directly oriented lox sites (pSAC114; FIG. 2). The KpnI-SacI region of pSAC114 (Seq. ID. No.4) was assembled in plasmid pSAC113, a pBluescript derivative. Starting from the left, the lox site located downstream of the Tpsba(L) terminator is contained in a KpnI-Bg1II fragment (SEQ ID NO:2). The fragment was obtained by annealing the complementary oligonucleotides: loxdel1T (SEQ ID NO: 10)5′-GGTACCATAACTTCGTATAATGTATGCTATACGAAGTTATAGATCT-3′ and loxdel1L (SEQ ID NO: 11)5′-AGATCTATAACTTCGTATAGCA TACATTATACGAAGTTATGGTACC-3′. The aadA gene derives from plasmid pZS176 (Prrn:RBS:aadA:TpsbA(L) (Svab and Maliga 1993) and it is contained in a HindIII-KpnI fragment. The lox site located upstream of aadA is contained in a Bg1II-HindIII fragment (SEQ ID NO: 1) and was obtained by annealing the complementary oligonucleotides: loxdel2T (SEQ ID NO: 12)5′-AGATCTATAACTTCGTATAATGTATGCTATACGAAGTTATAAGCTT-3′ and loxdel2L (SEQ ID NO: 13)5′-AAGCTTATAACTTCGTATA GCATACATTATACGAAGTTATAGATCT-3′. The attB sequence was created from a PstI-SpeI oligonucleotide (SEQ ID NO: 3) by annealing the complementary oligonucleotides: attBPstI (SEQ ID NO: 14)5′-CTGCAGCCGCGGTGCGGGTGCCAGGGCGTGCCCTTGGGCTC CCCGGGCGCGTACTCCACTAGT-3′ and attBSpeI (SEQ ID NO: 15)5′-ACTAGTGGAGTACGCGCCCGGGGAGCCCAAGGGCACGCCCTGGCACCCGCACCGCGG CTGCAG-3′. The KpnI-SacI fragment from pSAC113 (SEQ ID NO: 4) was cloned into the ScaI site of pPRV1 (Zoubenko et al. 1994) which contains the rrn16 targeting region to create pSAC114 (FIG. 2).

Integrase Plasmids for Transient Expression of int Gene in Plastids

The int gene and attP region of Streptomyces phage phiC31 is contained in pSET152 (Wilkinson 2002). To clone the attP sequence and int gene the Bg1I fragment from pSET152 was introduced into pBS KS+ at the blunted SpeI site to create plasmid pKO81. To express the int from plastid expression signals, the integrase coding region (SEQ ID NO: 5), contained in a BamHI-XbaI fragment, was introduced into pZS176 to replace the aadA coding region and create plasmid pKO107 (SEQ ID NO: 5; FIG. 3). pKO107 does not contain DNA sequences to maintain the plasmid as an episomal element.

To restrict integrase expression to plastids an editing dependant int gene was created. pKO111was created by replacing the neo coding region from pSC4 (Chaudhuri and Maliga 1996) with the int coding region, contained in a NheI-XbaI fragment (SEQ ID NO: 5; FIG. 4). pKO111 has the ColE1 replication origin and therefore is not maintained as an episomal element in plastids. In contrast, plasmid pKO126 has both the ColE1 replication origin and the NICE1 sequences that allow episomal maintenance in plastids (Staub and Maliga 1995). Plasmid pKO126 was obtained by replacing the neo coding region with the integrase coding region, contained in an NcoI-XbaI fragment, in a modified version of plasmid pNICER1 (pJS146) (Staub and Maliga 1995) (XbaI blunt; SEQ ID NO: 5; FIG. 5).

Donor Vectors to Provide the neo Gene and attP Sequence for INT Catalyzed Integration

The donor vector provides the attP sequence and marker gene sequence (neo), necessary for integrase mediated integration into the plastid genome, as well as a gene of interest. The attP sequence was PCR amplified from pSET152 with primers: attPXhoI (SEQ ID NO: 16) 5′-CAACTCGAGCAATCGCCCTGGGTG-3′ and attPHindIII (SEQ ID NO: 17)5′-CAAAAGCTTCCCGGTCACAACCCCTTG-3′ and confirmed by sequencing (SEQ ID NO: 6). pKO102 is a donor vector that contains an attP sequence, a neo marker gene, a lox site and a MCS. The neo gene from pHK10 (Kuroda and Maliga 2001b) was contained in a SacI/HindIII blunt fragment and has been modified by blunting the XbaI site at the 3′ end of the coding region. The lox site is contained in a KpnI-Bg1II fragment (SEQ ID NO: 2). To remove the ampicillin resistance gene and the f1 replication origin, plasmid pKO102 was digested with the AhdI-SacI enzymes, blunted and ligated to create plasmid pKO103 (SEQ ID NO: 7; FIG. 6). A gene of interest can be added to the donor vector at the multiple cloning site sequence (MCS).

Recipient Transplastomic Tobacco Plants with an attB Sequence and a lox Site

Plastid transformation vector pSAC114 carries an attB sequence and an aadA gene flanked by two lox sites in direct orientation (FIG. 2). Plastid transformation using the biolistic protocol, selection of transplastomic tobacco clones (RMOP medium, 500 mg/L Spectinomycin dihydrochloride) and characterization of the transplastomic clones by DNA gel blot analysis has been described previously (Svab and Maliga 1993). Transformation with pSAC114 yielded a number of independently transformed transplastomic lines, of which 3 were purified to the homoplastomic state: Nt-pSAC114-2A, Nt-pSAC114-3B and Nt-pSAC114-5A. All three lines are considered identical other than that they have been generated independently. A uniform population of transformed plastid genomes in the transplastomic plants was verified by DNA gel blot analysis (FIG. 7). The aadA gene was removed by a plastid-targeted nuclear-encoded cre introduced by Agrobacterium transformation or pollination (Corneille et al. 2001; Hajdukiewicz et al. 2001). The plastid genome of the resulting plants contains only one lox site and an attB sequence (FIG. 8).

INT-mediated Integration of a neo Donor Vector into the Nt-pSAC114 attB Sequence

To test for integrase-mediated insertion of the neo gene, a donor vector (pKO103) and an int encoding vector (pKO107, pKO111 or pKO126) were introduced into the plastids of Nt-pSAC114 plants by the biolistic process (FIG. 9). Clones with an integrated donor vector were selected on kanamycin containing (25 mg/L or 50 mg/L) RMOP medium. Examples for clones which were obtained by integrase-mediated neo gene insertion are Nt-pSAC114-2B/pKO111, Nt-pSAC114-2A-5/pKO107 and Nt-pSAC114-3B-1/pKO107. Clone Nt-pSAC114-2B/pKO111 was obtained by INT-mediated integration expressed from pKO111, a plasmid carrying an editing dependent int (E-int), and ColE1 ori. Donor integration in the clones Nt-pSAC114-2A-5/pKO107 and Nt-pSAC114-3B-1/pKO107 was mediated by int expressed from plasmid pKO107 (no editing signals; ColE1 ori only).

Insertion of neo into the plastid genome was tested by PCR amplification (FIG. 10). Two separate PCR reactions were performed using 1) primers 136 (SEQ ID NO: 18) (aadA; 5′-CCGCCAGCGTTCATCCTGAGC-3′) and neoAL (SEQ ID NO: 19) (5′-TGACAGCCGGAACACGGCGGC-3′) or 2) primers neoAU (SEQ ID NO: 20) (5′-TGAAGAGCTTGGCGGCGAAT-3′) and 191 (SEQ ID NO: 21) (5′-GAGATGTAACTCCAGTTCC-3′). For PCR reaction 1 a 1 kb fragment was expected if neo integrated by attB-attP recombination. For PCR reaction 2 a 2 kb fragment was expected if integration of the neo gene occurred. Perfect reconstituted attL (SEQ ID NO: 8) and attR (SEQ ID NO: 9) sequences were confirmed in Nt-pSAC114-2B/pKO111 by direct sequencing of the amplification products (FIG. 11). Integration events were also confirmed in positive clones Nt-pSAC114-2A-5/pKO107 and Nt-pSAC114-3B-1/pKO107 by direct sequencing of PCR products. The primers used for sequencing the junctions were 191 (SEQ ID NO: 21), attPHindIII (SEQ ID NO: 17) and attPXhoI (SEQ ID NO: 16).

A transplastomic recipient line may be created by introducing the attB sequence into the plastid genome using spectinomycin resistance (aadA gene) as a selective marker. The aadA gene is flanked by directly oriented lox sites, so that it can be removed by CRE. An example for a vector suitable to obtain the progenitor of an attB recipient is plasmid pSAC114 (FIG. 2) (KpnI-SacI fragment; SEQ ID NO:4). The aadA gene may be removed by a nuclear-encoded CRE (Corneille et al. 2001), the product of which is shown in FIG. 12B. Tobacco plant lines with an attB site and a lox site (no aadA) are Nt-pSAC114-pKO30 and Nt-pSAC114-pKO31 (FIG. 8C).

Transient expression of the int gene may be obtained from multiple, alternative vectors. These vectors differ with respect to sequences that sustain replication: some have only sequences for replication in E. coli (ColE1 ori) but not in plastids (pKO107, FIG. 3; pKO111, FIG. 4), others have the ColE1 replication origin and plastid sequences that sustain episomal maintenance (Staub and Maliga 1994a) (pKO126, FIG. 5). The INT in plasmid pKO111 at its N-terminus is translationally fused with the psbL editing segment (Chaudhuri and Maliga 1996), so that translation of the Eint (edited INT) mRNA is dependent on conversion of an ACG codon into an AUG translation initiation codon by RNA editing. Editing-dependent int is not expressed in E. coli (prokaryotes) or in the plant's nucleus (Hoch et al. 1991; Maier et al. 1996; Bock et al. 1997; Chaudhuri and Maliga 1997). Expression of int in plasmids pKO107 and pKO126 is from (non-edited) plastid signals. The schematic design of transient INT vectors is shown in FIG. 12C.

Donor vectors contain an attP sequence, a marker gene, a lox site and a gene of interest (goi) (FIG. 12C). The donor vector will be provided at the same time as the int plasmid. INT mediated recombination between the attB and attP sequences will result in integration of the donor vector into the recipient plastid genome, as shown in FIG. 12D. After recombination, the plastid genome contains a lox site, an attL sequence, a marker gene, a second lox site, a goi and an attR sequence. The marker gene (all sequences between the lox sites) can be subsequently removed by a plastid-targeted CRE. The resulting plants contain one lox site, a goi and an attR sequence (FIG. 12E). The cre gene, and the linked marker gene, can then be crossed out in the seed progeny to obtain cre- and marker-free plants containing a goi in the plastid genome.

The general scheme for transient INT-mediated insertion of the Donor vector is depicted in FIG. 12. The marker gene or genes used for the introduction of attB is not limited to aadA, and the marker gene or genes carried by the Donor vector are not limited to the neo gene, but could be any gene that confers a selectable or screenable phenotype to the plant cell suitable to achieve plastid transformation.

A working example, in which the aadA marker gene has not been removed from the recipient plastid genome, is shown in FIG. 9A. The INT was transiently expressed from plasmids pKO107 and pKO111. The donor vector pKO103 contains an attP sequence, a neo gene as a selectable marker, a lox site, and no gene of interest (FIG. 9A). The product of stable integration of the neo gene in the plastid genome via attB and attP recombination is shown in FIG. 9B, and is described in Example 1. The plastid genome of resulting plants contain: an aadA gene flanked by two lox sites; an attL sequence; a neo gene; a third lox site in direct orientation with the other two lox sites; the ColE1 ori of the Bluescript plasmid, that is the backbone of the donor vector; and an attR sequence (FIG. 9B).

EXAMPLE 2 Site-specific Integration of Foreign DNA by a Plastid Encoded Integrase

In Example 2, we describe a method for integration of the donor vector by INT expressed from a gene stably integrated in the plastid genome. Stable plastid expression of int may yield higher levels of INT resulting in an increase in integration efficiency as compared to transiently expressed INT, which was described in Example 1. Example 2 describes two systems for stable expression of the plastid int gene yielding the same result, a gene of interest, one lox site and attR sequence incorporated in the plastid genome. The two systems differ with respect to the number of marker genes required (System 2A requires one, whereas 2B requires two marker genes) and flexibility to choose the promoter for the expression of gene of interest (2A, no flexibility; 2B, flexible).

System 2A calls for a recipient with a plastid-encoded integrase flanked by a lox site and an attB sequence (FIG. 13B). The recipient may be created by transformation with the plastid vector shown in FIG. 13A. The aadA-int dicistronic operon shown in FIG. 13A is expressed in a cassette with P1 and T1, a plastid promoter and terminator. In this construct the aadA coding region is flanked by two lox sites in direct orientation and the pt-int coding region is cloned next to it. An attB sequence is cloned downstream of the T1 terminator to facilitate INT-mediated integration of the donor vector. The desired recipient is obtained by CRE-mediated excision of the aadA coding region (FIG. 13B). The int gene is now located directly downstream of P1 from which it is expressed. Segregating out the nuclear cre gene in the seed progeny completes construction of the recipient for System 2A.

The donor vector for System 2A carries the attP sequence, a plastid-selectable marker gene (mg), a lox site and a goi (FIG. 13C. This donor vector is a derivative of pKO103 (FIG. 6; SEQ ID NO:7) which lacks a goi. The marker gene has its own expression signals (P2, T2); the goi has only a RBS and T3 sequence. INT-mediated integration events are selected by the expression of the marker gene carried by the donor vector. This marker gene can be any selectable marker, as the recipient no longer carries a marker gene. Integration results in the insertion of the donor plasmid at the attB site (FIG. 13D). The marker gene and the integrase are subsequently removed by CRE. This will result in expression of the goi from the P1 promoter (FIG. 13E). Cre will then be segregated out from the plants in the seed progeny as a final step to obtain the desired end product. The P1, P2 and T1, T2 and T3 are variants of plastid expression signals. Some examples of promoter and terminator sequences that could be used are: Prrn, PsbA, ptrnV and TpsbA, TrbcL, Trps16 described in (Staub and Maliga 1993; Svab and Maliga 1993; Staub and Maliga 1994b; Zoubenko et al. 1994), U.S. Pat. No. 5,877,402.

System 2B is based on a recipient in which int and aadA are expressed as a dicistronic operon (FIG. 14A). The donor plasmid for System 2B is the same as for System 2A, except that the goi has its own promoter (P3). Clones carrying the integrated donor are selected by expression of the marker gene (for example neo, as shown in FIG. 14). INT-mediated integration yields a complex structure shown in FIG. 14C. The desired end product, a plastid genome containing the goi, is obtained by CRE-mediated excision of int, aadA and the neo genes (FIG. 14D). Segregating out the nuclear cre gene in the seed progeny completes construction of the recipient for System 2B.

EXAMPLE 3 Site-specific Integration of Foreign DNA into the Plastid Genome Facilitated by a Nuclear-encoded Plastid Targeted int

The following materials and methods are provided to facilitate the practice of Example 3.

Plastid Targeted N-int Linked to a Nuclear Gentamycin Resistance Gene

The N-int gene in Agrobacterium vector pKO117 encodes INT with its N terminus translationally fused with the pea Rubisco small subunit (SSU) chloroplast transit peptide (Timko et al. 1985) and twenty-two amino acids of the mature Rubisco small subunit. The int coding region is contained in an NcoI-XbaI fragment (SEQ ID NO: 5). Plasmid pKO117 was obtained by replacing the cre coding region with the int coding region in plasmid pKO30 (WO01/21768). The map of Agrobacterium transformation vector pKO117 is shown in FIG. 15.

To obtain suitable recipients, transformation of Nt-pSAC114 transplastomic lines (Example 1) was carried out with Agrobacterium vector pKO117. Transformation and tobacco plant regeneration was carried out as described (Hajdukiewicz et al. 1994). Briefly, nuclear gene transformants were selected by gentamycin resistance on RMOP shoot regeneration medium containing 100 mg/L gentamycin and 500 mg/L carbenicillin. Gentamycin resistance of the shoots was confirmed by rooting on plant maintenance (RM) medium containing 100 mg/L gentamycin. These plants contain an attB site and a lox site in the plastid genome and express an N-int in the nucleus, are suitable recipients for transformation with suitable donor vectors of the invention.

The system described in Example 3 relies on a nuclear-encoded, plastid-targeted integrase gene (N-int) for INT activity in plastids. The only difference between the systems described in Example 1 and Example 3 is that in Example 1 INT is provided by a plastid construct transiently expressed in plastids whereas in Example 3 it is provided by a nuclear gene. The transplastomic recipient line carries an attB sequence and a lox site, as shown for Example 1. The donor vector contains an attP sequence, a marker gene, a lox site and a gene of interest (goi) (FIG. 16B). The donor vector is introduced into the plastids by a suitable method (biolistic transformation, PEG treatment, and electroporation), and clones carrying the insertion are selected by the marker gene encoded in the donor vector (FIG. 16C). The marker gene or genes in the donor vector can be any gene that confers a selectable or screenable phenotype to the plant cell suitable to achieve plastid transformation. The marker gene and attL are subsequently removed by a nuclear-encoded plastid-targeted CRE. The resulting plants contain one lox site, a goi and an attR sequence (FIG. 16D). The cre gene, and the linked marker gene, can then be crossed out in the seed progeny to obtain cre-and marker-free plants containing a goi in the plastid genome.

EXAMPLE 4 Introduction of the Bar Gene into the Plastid Genome Using INT

The INT site-specific integrase is a useful enzyme to efficiently incorporate the transforming DNA into the plastid genome. Example 4 describes incorporation of a bar gene into the plastid genome using the integrase system. The bar gene has been shown to confer herbicide resistance to transplastomic plants (Lutz et al. 2001). In this example, incorporation of a bar is exemplified in the plastid genome from a suitable donor vector. INT activity for integration can be provided by any of the methods described in this application, from a transient or stable int expressed in the plastid or nuclear genetic compartments.

As described herein, introduction of bar is accomplished using two different recipients. One of the recipients has a lox site and an attB site, i.e., the same recipient that was used in Example 1 and Example 3, shown in FIG. 12B, FIG. 16A and FIG. 17A. The donor vector is shown in FIG. 17B, and is identical with donor vector shown in FIGS. 12C and 16B except, that bar is the gene of interest. Plastid genomes with integrated copies of the bar donor vector can be selected by the expression of the marker gene conferring resistance to spectinomycin, streptomycin, (Svab et al. 1990; Svab and Maliga 1993) kanamycin (Carrer et al. 1993) or resistance to betaine aldehyde (Daniell et al. 2001). After the marker gene and bar gene integrate into the plastid genome by attP-attB mediated recombination (FIG. 17C), the marker gene and the attL site can be removed by a variety of methods. These include introducing the nuclear cre gene into the plants by crossing, direct Agrobacterium transformation, transiently expressing CRE from a DNA or RNA template, or introducing the CRE enzyme directly by microinjection. The plastid genome after removal of the marker gene is shown in FIG. 17D. If a stably integrated cre was used, the nuclear cre gene will be removed by segregation in the seed progeny.

The second recipient, in addition to a lox site and attB sequence, has a permanently incorporated plastid promoter P1 transcribing the lox sequence and attB (FIG. 18B). Transcription of the attB sequence may enhance integration efficiency. The marker gene and the bar gene (or other genes of interest) in the bar donor vector are expressed as a dicistronic operon with an RBS and a lox site upstream of bar (FIG. 18C). Integration events are selected by expression of the marker gene, which is subsequently removed by the CRE.

The second recipient is compatible with a variant of the dicistronic donor vector, in which the plastid marker gene has no functional promoter (FIG. 18D). The plastid marker of this donor vector is not expressed in E. coli, therefore the ampicillin resistance gene in this vector cannot be removed. Integration of the donor vector at the attB site results in expression of the marker gene and of the bar gene. The marker gene is subsequently removed by CRE (FIG. 18G), resulting in the bar gene expressing from the P1 promoter incorporated in the plastid genome. The nuclear cre gene is removed by segregation in the seed progeny. The advantage of the system is that it requires only one functional plastid promoter.

EXAMPLE 5 Elimination of Marker Genes Using a Negative Selection Scheme for Transient Expression of CRE

To decrease the time necessary for the CRE-mediated elimination of marker genes from the plastid genome a negative selection scheme is provided herein. In this Example, we use only transiently expressed CRE recombinase for the removal of DNA sequences. Transiently expressing CRE will eliminate the need to stably integrate cre into the plant genome and remove it after deletion has occurred. Because transiently expressed CRE not expected to eliminate all DNA sequences, a negative selection scheme must be used so that genome copies, which lack a negative selective marker, are preferentially maintained. CRE can be expressed transiently either from a plastid gene encoded in a non-integrating vector or from a non-integrated nuclear gene which is fused to a transit peptide. One example of a negative selection marker gene is the codA gene. codA is bacterial gene encoding cytosine deaminase (CD; EC 3.5.4.1), which is absent in plants. Expression of codA plastids make tobacco cells sensitive to 5-fluorocytosine (5FC) (Serino and Maliga 1997). Thus, 5FC resistance can be used for positive identification of cells with CRE-induced codA deletion, even if the deletion events are relatively rare (Corneille et al. 2001) In one embodiment, the codA is translationally fused with a positive selectable marker. The aadA gene accepts C-terminal fusions, thus aadA C-terminus may be translationally fused with the codA N-terminus by replacing the gfp coding region in plasmid pMSK56 or pMSK57 (Khan and Maliga 1999) from plasmid pGS104 or pGS107 (Serino and Maliga 1997) as NcoI-XbaI fragments. The neo gene does not accept C-terminal fusions, thus the codA C-terminus should be fused with the neo N-terminus. If necessary, protein stability may be improved by including a 16-mer flexible junction peptide between the proteins, such as (SEQ ID NO: 28) ELVEGKLELVEGLKVA (SEQ ID NO: 22; 5′GAACTTGTTGAAGAAAATTGGAGCTAGTAGAAGGTCTTAAAGTCGCC-3′) reported for the aadA-gfp fusion protein (Khan and Maliga 1999) (WO 00/07421). Depending on the nature of the fusion proteins, shorter (10-mer) and longer flexible junction peptides may be suitable to link CD and the protein that confers the selectable phenotype. A suitable 10-mer peptide would be (SEQ ID NO: 29) ELAVEGKLEA encoded in (SEQ ID NO: 23) 5′-GAACTTGCAGTTGAAGGAAAATTGGAGGCC-3′.

The recipient plastid genome has a lox site and an attB site, and it is the same recipient that was used in Example 1, Example 3 and Example 4, and is shown in FIG. 12B, FIG. 16A, FIG. 17A and FIG. 19A. The donor vector is also shown in FIG. 19B, and is identical with donor vector shown in FIG. 12C except, that the marker gene encodes an AAD-CD fusion protein encoded in an aadA:codA fusion gene. Plastid genomes with integrated donor copies are selected by spectinomycin resistance. When the homoplastomic state is achieved, CRE is transiently expressed in the plastid and initiates aadA:codA excision. The product of excision, a plastid genome with a lox site, a gene of interest and an attR sequence, is shown in FIG. 19D. Clonal lines in which aadA:codA has been excised can be positively identified by 5FC resistance.

EXAMPLE 6 Plastid Transformation and Elimination of Marker Genes Relying on Transiently Expressed Site-specific Recombinases and a Negative Selection Scheme

In vegetatively propagated crops, such as fruit trees, strawberries, ornamental plants, forest trees, and potato going through a seed progeny is prohibitive as these plants are highly heterozygous and it would not be possible to recover the original commercial cultivars in the seed progeny. Engineering the plastid genome of these crops may be accomplished by transiently expressed site-specific recombinases as set forth in this example.

Integration of donor sequences will be accomplished by relying on natural attB or attP sites that may be identified empirically by integration of donor vector in plastids with INT activity. Such functional att sites have been identified in the human and mouse nuclear genomes (Thyagarajan 2001). Clones with integrated copies of the donor vector will be identified by the expression of a positive marker gene. The marker genes may confer resistance to spectinomycin, streptomycin, (Svab et al. 1990; Svab and Maliga 1993) kanamycin (Carrer et al. 1993) or resistance to betaine aldehyde (Daniell et al. 2001) (GenBank Accession No. M31480). Plastid transformants may also be selected by utilization of sugars, such as mannose, bu expression of the enzyme phosphomannose isomerase (ManA) (Joersboro et al. 1998; Negrotto et al. 2000) or on xylose by expression of xylose isomerase (XylA) in chloroplasts (Haldrup et al. 1998). The bar gene, conferring PPT resistance (Lutz et al. 2001); aacC1 gene, conferring gentamycin resistance (Carrer et al. 1990) and hph (hygromycin phosphotransferase) conferring hygromycin resistance (SEQ ID NO: 24) (Gritz and Davies 1983) (GenBank Accession No. K01193) are not suitable for direct selection of transplastomic clones, but will confer resistance to plant cells when most genome copies have been altered. The coding region of the genes may be fused with AAD, NPTII or the BDH proteins, which are suitable for direct selection at the early stage of plastid transformation. Methods for protein fusion and suitable flexible linkers to link proteins encoded by the marker genes are described in Example 5. Selection for PPT resistance, gentamycin resistance or hygromycin resistance may be used to advantage at a later stage of plastid transformation when most plastid genome copies have been transformed.

The integrated marker gene sequences are subsequently removed by transiently expressing CRE, and selection for a negative marker, as described in Example 5. Transient expression of the site-specific recombinases, INT and CRE, will facilitate expression of agronomically important traits in the plastid genome of vegetatively propagated crops without the selectable marker gene.

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Appendix I

The following sequences were utilized in practicing the methods of the present invention.

Seq. ID No. 1 lox site (BglII-HindIII) AGATCTATAACTTCGTATAATGTATGCTATACGAAGTTATAAG CTT Seq. ID No. 2 lox site (KpnI-BglII) GGTACCATAACTTCGTATAATGTATGCTATACGAAGTTATAGA TCT Seq. ID No. 3 attB sequence (PstI-SpeI) CTGCAGCCGCGGTGCGGGTGCCAGGGCGTGCCCTTGGGCTCCC CGGGCGCGTACTCCACTAGT Seq. ID No. 4 pSAC113 (KpnI-SacI) GGTACCATAACTTCGTATAATGTATGCTATACGAAGTTATAGA TCAGCTTGCATGCCTGCAGGTCGAATATAGCTCTTCTTTCTTA TTTCAATGATATTATTATTTCAAAGATAAGAGATATTCAAAGA TAAGAGATAAGAAGAAGTCAAAATTTGATTTTTTTTTTGGAAA AAAAAAATCAAAAAGATATAGTAACATTAGCAAGAAGAGAAAC AAGTTCTATTTCACAATTTAAACAAATACAAAATCAAAATAGA ATACTCAATCATGAATAAATGCAAGAAAATAACCTCTCCTTCT TTTTCTATAATGTAAACAAAAAAGTCTATGTAAGTAAAATACT AGTAAATAAATAAAAAGAAAAAAAGAAAGGAGCAATAGCACCC TCTTGATAGAACAAGAAAATGATTATTGCTCCTTTCTTTTCAA AACCTCCTATAGACTAGGCCAGGATCGCTCTAGACATTATTTG CCGACTACCTTGGTGATCTCGCCTTTCACGTAGTGGACAAATT CTTCCAACTGATCTGCGCGCGAGGCCAAGCGATCTTCTTCTTG TCCAAGATAAGCCTGTCTAGCTTCAAGTATGACGGGCTGATAC TGGGCCGGCAGGCGCTCCATTGCCCAGTCGGCAGCGACATCCT TCGGCGCGATTTTGCCGGTTACTGCGCTGTACCAAATGCGGGA CAACGTAAGCACTACATTTCGCTCATCGCCAGCCCAGTCGGGC GGCGAGTTCCATAGCGTTAAGGTTTCATTTAGCGCCTCAAATA GATCCTGTTCAGGAACCGGATCAAAGAGTTCCTCCGCCGCTGG ACCTACCAAGGCAACGCTATGTTCTCTTGCTTTTGTCAGCAAG ATAGCCAGATCAATGTCGATCGTGGCTGGCTCGAAGATACCTG CAAGAATGTCATTGCGCTGCCATTCTCCAAATTGCAGTTCGCG CTTAGCTGGATAACGCCACGGAATGATGTCGTCGTGCACAACA ATGGTGACTTCTACAGCGCGGAGAATCTCGCTCTCTCCAGGGG AAGCCGAAGTTTCCAAAAGGTCGTTGATCAAAGCTCGCCGCGT TGTTTCATCAAGCCTTACGGTCACCGTAACCAGCAAATCAATA TCACTGTGTGGCTTCAGGCCGCCATCCACTGCGGAGCCGTACA AATGTACGGCCAGCAACGTCGGTTCGAGATGGCGCTCGATGAC GCCAACTACCTCTGATAGTTGAGTCGATACTTCGGCGATCACC GCTTCCCCCATGGATCCCTCCCTACAACTGTATCCAAGCGCTT CGAATTCGCCCGGAGTTCGCTCCCAGAAATATAGCCATCCCTG CCCCCTCACGTCAATCCCACGAGCCTCTTATCCATTCTCATTG AACGACGGCGGGGGAGCGGATCTATAACTTCGTATAATGTATG CTATACGAAGTTATAAGCTTGATATCGAATTCCTGCAGCCGCG GTGCGGGTGCCAGGGCGTGCCCTTGGGCTCCCCGGGCGCGTAC TCCACTAGTTCTAGAGCGGCCGCCACCGCGGTGGAGCTC Seq. ID No. 5 int coding region (BamHI-XbaI) GGATCCATGGCTAGCGACACGTACGCGGGTGCTTACGACCGTC AGTCGCGCGAGCGCGAAAATTCGAGCGCAGCAAGCCCAGCGAC ACAGCGTAGCGCCAACGAAGACAAGGCGGCCGACCTTCAGCGC GAAGTCGAGCGCGACGGGGGCCGGTTCAGGTTCGTCGGGCATT TCAGCGAAGCGCCGGGCACGTCGGCGTTCGGGACGGCGGAGCG CCCGGAGTTCGAACGCATCCTGAACGAATGCCGCGCCGGGCGG CTCAACATGATCATTGTCTATGACGTGTCGCGCTTCTCGCGCC TGAAGGTCATGGACGCGATTCCGATTGTCTCGGAATTGCTCGC CCTGGGCGTGACGATTGTTTCCACTCAGGAAGGCGTCTTCCGG CAGGGAAACGTCATGGACCTGATTCACCTGATTATGCGGCTCG ACGCGTCGCACAAAGAATCTTCGCTGAAGTCGGCGAAGATTCT CGACACGAAGAACCTTCAGCGCGAATTGGGCGGGTACGTCGGC GGGAAGGCGCCTTACGGCTTCGAGCTTGTTTCGGAGACGAAGG AGATCACGCGCAACGGCCGAATGGTCAATGTCGTCATCAACAA GCTTGCGCACTCGACCACTCCCCTTACCGGACCCTTCGAGTTC GAGCCCGACGTAATCCGGTGGTGGTGGCGTGAGATCAAGACGC ACAAACACCTTCCCTTCAAGCCGGGCAGTCAAGCCGCCATTCA CCCGGGCAGCATCACGGGGCTTTGTAAGCGCATGGACGCTGAC GCCGTGCCGACCCGGGGCGAGACGATTGGGAAGAAGACCGCTT CAAGCGCCTGGGACCCGGCAACCGTTATGCGAATCCTTCGGGA CCCGCGTATTGCGGGCTTCGCCGCTGAGGTGATCTACAAGAAG AAGCCGGACGGCACGCCGACCACGAAGATTGAGGGTTACCGCA TTCAGCGCGACCCGATCACGCTCCGGCCGGTCGAGCTTGATTG CGGACCGATCATCGAGCCCGCTGAGTGGTATGAGCTTCAGGCG TGGTTGGACGGCAGGGGGCGCGGCAAGGGGCTTTCCCGGGGGC AAGCCATTCTGTCCGCCATGGACAAGCTGTACTGCGAGTGTGG CGCCGTCATGACTTCGAAGCGCGGGGAAGAATCGATCAAGGAC TCTTACCGCTGCCGTCGCCGGAAGGTGGTCGACCCGTCCGCAC CTGGGCAGCACGAAGGCACGTGCAACGTCAGCATGGCGGCACT CGACAAGTTCGTTGCGGAACGCATCTTCAACAAGATCAGGCAC GCCGAAGGCGACGAAGAGACGTTGGCGCTTCTGTGGGAAGCCG CCCGACGCTTCGGCAAGCTCACTGAGGCGCCTGAGAAGAGCGG CGAACGGGCGAACCTTGTTGCGGAGCGCGCCGACGCCCTGAAC GCCCTTGAAGAGCTGTACGAAGACCGCGCGGCAGGCGCGTACG ACGGACCCGTTGGCAGGAAGCACTTCCGGAAGCAACAGGCAGC GCTGACGCTCCGGCAGCAAGGGGCGGAAGAGCGGCTTGCCGAA CTTGAAGCCGCCGAAGCCCCGAAGCTTCCCCTTGACCAATGGT TCCCCGAAGACGCCGACGCTGACCCGACCGGCCCTAAGTCGTG GTGGGGGCGCGCGTCAGTAGACGACAAGCGCGTGTTCGTCGGG CTCTTCGTAGACAAGATCGTTGTCACGAAGTCGACTACGGGCA GGGGGCAGGGAACGCCCATCGAGAAGCGCGCTTCGATCACGTG GGCGAAGCCGCCGACCGACGACGACGAAGACGACGCCCAGGAC GGCACGGAAGACGTAGCGGCGTAGTCTAGA Seq. ID No. 6 attP sequence (XhoI-HindIII) CTCGAGCAATCGCCCTGGGTGGGTTACACGACGCCCCTCTATG GCCCGTACTGACGGACACACCGAAGCCCCGGCGGCAACCCTCA GCGGATGCCCCGGGGCTTCACGTTTTCCCAGGTCAGAAGCGGT TTTCGGGAGTAGTGCCCCAACTGGGGTAACCTTTGAGTTCTCT CAGTTGGGGGCGTAGGGTCGCCGACATGACACAAGGGGTTGTG ACCGGGAAGCTT Seq. ID No. 7 pKO103 (AhdI-SacI) CCACCGCGGTGGCGGCCGCTCTAGAACTAGTGGATCCCCCGGG CTGCAGGAATTCGATATCAAGCTTATCGATACCGTCGACAGAT CTATAACTTCGTATAGCATACATTATACGAAGTTATGATCAAG CTAGCTTGCTAGATTTTGTATTTCAAATCTTGTATATCTAGGT AAGTATATHNDACTTAGTCAAAATATATGCAATAGAATCTTTG TTGTATTCGGCTCAATCCTTTTAGTAAAAGATTGGGCCGAGTT TAATTGCAATTCAATTAAGAGAACGAAGGATAATTACTTGAGT TCTTTCTCCTTATCCTTCTTTATTTCCTGCTAATTTATCTGCT AATGTCTACTCTAGCTACACCCGCTCAGAAGAACTCGTCAAGA TVAGGCGATAGAAGGCGATGCGCTGCGAATCGGGAGCGGCGAT ACCGTAAAGCACGAGGAAGCGGTCAGCCCATTCGCCGCCAAGC TCTTCAGCAATATCACGGGTAGCCAACGCTATGTCCTGATAGC GGTCCGCCACACCCAGCCGGCCACAGTCGATGAATCCAGAAAA GCGGCCATTTTCCACCATGATATTCGGCAAGCAGGCATCGCCA TGTGTCACGACGAGATCCTCGCCGTCGGGCATGCGCGCCTTGA GCCTGGCGAACAGTTCGGCTGGCGCGAGCCCCTGATGCTCTTC GTCCAGATCATCCTGATCGACAAGACCGGCTTCCATCCGAGTA CGTGCTCGCTCGATGCGATGTTTCGCTTGGTGGTCGAATGGGC AGGTAGCCGGATCAAGCGTATGCAGCCGCCGCATTGCATCAGC CATGATGGATACTTTCTCGGCAGGAGCAAGGTGAGATGACAGG AGATCCTGCCCCGGCACTTCGCCCAATAGCAGCCAGTCCCTTC CCGCTTCAGTGACAACGTCGAGCACAGCTGCGCAAGGAACGCC CGTCGTGGCCAGCCACGATAGCCGCGCTGCCTCGTCCTGGAGT TCATTCAGGGCACCGGACAGGTCGGTCTTGACAAAAAGAACCG GGCGCCCCTGCGCTGACAGCCGGAACACGGCGGCATCAGAGCA GCCGATTGTCTGTTGTGCCCAGTCATAGCCGAATAGCCTCTCC ACCCAAGCGGCCGGAGAACCTGCGTGCAATCCATCTTGTTCAA TGCTAGCCGTGGAAACCCCAGAACCAGADNAGTAGTAGGATTG ATTCTCATAATAATAAAATAAATAAATATGTCGAAATGTTTTT GCAAAAATTATCGAATTTAAAATAAATGTCCGCTTGCACGTCG ATCGGTTAATTCTCCCAGAAATATAGCCATCCCTGCCCCCTCA CGTCAATCCCACGAGCCTCTTATCCATTCTCATTGAACGACGG CGGGGGAGCGAGCTTCCCGGTCACAACCCCTTGTGTCATGTCG GCGACCCTACGCCCCCAACTGAGAGAACTCAAAGGTTACCCCA GTTGGGGCACTACTCCCGAAAACCGCTTCTGACCTGGGAAAAC GTGAAGCCCCGGGGCATCCGCTGAGGGTTGCCGCCGGGGCTTC GGTGTGTCCGTCAGTACGGGCCATAGAGGGGCGTCGTGTAACC CACCCAGGGCGATTGCTCGACCAGCTTTTGTTCCCTTTAGTGA GGGTTAATTGCGCGCTTGGCGTAATCATGGTCATAGCTGTTTC CTGTGTGAAATTGTTATCCGCTCACAATTCCACACAACATACG AGCCGGAAGCATAAAGTGTAAAGCCTGGGGTGCCTAATGAGTG AGCTAACTCACATTAATTGCGTTGCGCTCACTGCCCGCTTTCC AGTCGGGAAACCTGTCGTGCCAGCTGCATTAATGAATCGGCCA ACGCGCGGGGAGAGGCGGTTTGCGTATTGGGCGCTCTTCCGCT TCCTCGCTCACTGACTCGCTGCGCTCGGTCGTTCGGCTGCGGC GAGCGGTATCAGCTCACTCAAAGGCGGTAATACGGTTATCCAC AGAATCAGGGGATAACGCAGGAAAGAACATGTGAGCAAAAGGC CAGCAAAAGGCCAGGAACCGTAAAAAGGCCGCGTTGCTGGCGT TTTTCCATAGGCTCCGCCCCCCTGACGAGCATCACAAAAATCG ACGCTCAAGTCAGAGGTGGCGAAACCCGACAGGACTATAAAGA TACCAGGCGTTTCCCCCTGGAAGCTCCCTCGTGCGCTCTCCTG TTCCGACCCTGCCGCTTACCGGATACCTGTCCGCCTTTCTCCC TTCGGGAAGCGTGGCGCTTTCTCATAGCTCACGCTGTAGGTAT CTCAGTTCGGTGTAGGTCGTTCGCTCCAAGCTGGGCTGTGTGC ACGAACCCCCCGTTCAGCCCGACCGCTGCGCCTTATCCGGTAA CTATCGTCTTGAGTCCAACCCGGTAAGACACGACTTATCGCCA CTGGCAGCAGCCACTGGTAACAGGATTAGCAGAGCGAGGTATG TAGGCGGTGCTACAGAGTTCTTGAAGTGGTGGCCTAACTACGG CTACACTAGAAGGACAGTATTTGGTATCTGCGCTCTGCTGAAG CCAGTTACCTTCGGAAAAAGAGTTGGTAGCTCTTGATCCGGCA AACAAACCACCGCTGGTAGCGGTGGTTTTTTTGTTTGCAAGCA GCAGATTACGCGCAGAAAAAAAGGATCTCAAGAAGATCCTTTG ATCTTTTCTACGGGGTCTGACGCTCAGTGGAACGAAAACTCAC GTTAAGGGATTTTGGTCATGAGATTATCAAAAAGGATCTTCAC CTAGATCCTTTTAAATTAAAAATGAAGTTTTAAATCAATCTAA AGTATATATGAGTAAACTTGGTCTGACAGTTACCAATGCTTAA TCAGTGAGGCACCTATCTCAGCGATCTGTCTATTTCGTTCATC CATAGTTGCCTGACTCC Seq. ID No. 8 attL sequence AGCCGCGGTGCGGGTGCCAGGGCGTGCCCTTGAGTTCTCTCAG TTGGGGGCGTAGGGTCGCCGACATGACACAAGGGGTTGTGACC GGG Seq. ID No. 9 attR sequence GAGCAATCGCCCTGGGTGGGTTACACGACGCCCCTCTATGGCC CGTACTGACGGACACACCGAAGCCCCGGCGGCAACCCTCAGCG GATGCCCCGGGGCTTCACGTTTTCCCAGGTCAGAAGCGGTTTT CGGGAGTAGTGCCCCAACTGGGGTAACCTTTGGGCTCCCCGGG CGCGTACTCCAC Seq. ID No. 10 loxdel1T 5′-GGTACCATAACTTCGTATAATGTATGCTATACGAAGTTAT AGATCT-3′ Seq. ID No. 11 loxdel1L 5′-AGATCTATAACTTCGTATAGCATACATTATACGAAGTTAT GGTACC-3′ Seq. ID No. 12 loxde12T 5′-AGATCTATAACTTCGTATAATGTATGCTATACGAAGTTAT AAGCTT-3′ Seq. ID No. 13 loxde12L 5′-AAGCTTATAACTTCGTATAGCATACATTATACGAAGTTAT AGATCT-3′ Seq. ID No. 14 attBPstI 5′-CTGCAGCCGCGGTGCGGGTGCCAGGGCGTGCCCTTGGGCT CCCCGGGCGCGTACTCCACTAGT-3′ Seq. ID No. 15 attBSpeI 5′-ACTAGTGGAGTACGCGCCCGGGGAGCCCAAGGGCACGCCC TGGCACCCGCACCGCGGCTGCAG-3′ Seq. ID No. 16 attPXhoI 5′-CAACTCGAGCAATCGCCCTGGGTG-3′ Seq. ID No. 17 attPHindIII 5′-CAAAAGCTTCCCGGTCACAACCCCTTG-3′ Seq. ID No. 18 Primer 136 5′-CCGCCAGCGTTCATCCTGAGC-3′ Seq. ID No. 19 neoAL 5′-TGACAGCCGGAACACGGCGGC-3′ Seq. ID No. 20 neoAU 5′-TGAAGAGCTTGGCGGCGAAT-3′ Seq. ID No. 21 Primer 191 5′-GAGATGTAACTCCAGTTCC-3′ Seq. ID No. 22; 16-mer junction peptide 5′-GAACTTGTTGAAGGAAAATTGGAGCTAGTAGAAGGTCTTA AAGTCGCC-3′ Seq. ID No. 23; 10-mer junction peptide 5′-GAACTTGCAGTTGAAGGAAAATTGGAGGCC-3′. Seq. ID No. 24 Plastid hph sequence ccATGgctag cAAAAAGCCT GAACTCACCG CGACGTCTGT CGAGAAGTTT CTGATCGAAA AGTTCGACAG CGTCTCCGAC CTGATGCAGC TCTCGGAGGG CGAAGAATCT CGTGCTTTCA GCTTCGATGT AGGAGGGCGT GGATATGTCC TGCGGGTAAA TAGCTGCGCC GATGGTTTCT ACAAAGATCG TTATGTTTAT CGGCACTTTG CATCGGCCGC GCTCCCGATT CCGGAAGTGC TTGACATTGG GGAATTtAGC GAGAGCCTGA CCTATTGCAT CTCCCGCCGT GCACAGGGTG TCACGTTGCA AGACCTGCCT GAAACCGAAC TGCCCGCTGT TCTGCAGCCG GTCGCGGAGG CtATGGATGC GATCGCTGCG GCCGATCTTA GCCAGACGAG CGGGTTCGGC CCATTCGGAC CGCAAGGAAT CGGTCAATAC ACTACATGGC GTGATTTCAT ATGCGCGATT GCTGATCCCC ATGTGTATCA CTGGCAAACT GTGATGGACG ACACCGTCAG TGCGTCCGTC GCGCAGGCTC TCGATGAGCT GATGCTTTGG GCCGAGGACT GCCCCGAAGT CCGGCACCTC GTGCACGCGG ATTTCGGCTC CAACAATGTC CTGACGGACA ATGGCCGCAT AACAGCGGTC ATTGACTGGA GCGAGGCGAT GTTCGGGGAT TCCCAATACG AGGTCGCCAA CATCTTCTTC TGGAGGCCGT GGTTGGCTTG TATGGAGCAG CAGACGCGCT ACTTCGAGCG GAGGCATCCG GAGCTTGCAG GATCGCCGCG GCTCCGGGCG TATATGCTCC GCATTGGTCT TGACCAACTC TATCAGAGCT TGGTTGACGG CAATTTCGAT GATGCAGCTT GGGCGCAGGG TCGATGCGAC GCAATCGTCC GATCCGGAGC CGGGACTGTC GGGCGTACAC AAATCGCCCG CAGAAGCGCG GCCGTCTGGA CCGATGGCTG TGTAGAAGTA CTCGCCGATA GTGGAAACCG ACGCCCCAGC ACTCGTCCtc GaGCAAAGGA ATAGatctag a Seq. ID No. 25. Int gene in plasmid pKO107 (SacI-HindIII) gagctcggta ccGCTCCCCC GCCGTCGTTC AATGAGAATG GATAAGAGGC TCGTGGGATT GACGTGAGGG GGCAGGGATG GCTATATTTC TGGGAGCGAA CTCCGGGCGA ATtcGAAGCG CtTGGATACA GTTGTAGGGA GGGATCCATG GCTAGCgaca cgtacgcggg tgcttacgac cgtcagtcgc gcgagcgcga Aaattcgagc gcagcaagcc cagcgacaca gcgtagcgcc aacgaagaca aggcggccga ccttcagcgc gaagtcgagc gcgacggggg ccggttcagg ttcgtcgggc atttcagcga agcgccgggc acgtcggcgt tcgggacggc ggagcgcccg gagttcgaac gcatcctgaa cgaatgccgc gccgggcggc tcaacatgat cattgtctat gacgtgtcgc gcttctcgcg cctgaaggtc atggacgcga ttccgattgt ctcggaattg ctcgccctgg gcgtgacgat tgtttccact caggaaggcg tcttccggca gggaaacgtc atggacctga ttcacctgat tatgcggctc gacgcgtcgc acaaagaatc ttcgctgaag tcggcgaaga ttctcgacac gaagaacctt cagcgcgaat tgggcgggta cgtcggcggg aaggcgcctt acggcttcga gcttgtttcg gagacgaagg agatcacgcg caacggccga atggtcaatg tcgtcatcaa caagcttgcg cactcgacca ctccccttac cggacccttc gagttcgagc ccgacgtaat ccggtggtgg tggcgtgaga tcaagacgca caaacacctt cccttcaagc cgggcagtca agccgccatt cacccgggca gcatcacggg gctttgtaag cgcatggacg ctgacgccgt gccgacccgg ggcgagacga ttgggaagaa gaccgcttca agcgcctggg acccggcaac cgttatgcga atccttcggg acccgcgtat tgcgggcttc gccgctgagg tgatctacaa gaagaagccg gacggcacgc cgaccacgaa gattgagggt taccgcattc agcgcgaccc gatcacgctc cggccggtcg agcttgattg cggaccgatc atcgagcccg ctgagtggta tgagcttcag gcgtggttgg acggcagggg gcgcggcaag gggctttccc gggggcaagc cattctgtcc gccatggaca agctgtactg cgagtgtggc gccgtcatga cttcgaagcg cggggaagaa tcgatcaagg actcttaccg ctgccgtcgc cggaaggtgg tcgacccgtc cgcacctggg cagcacgaag gcacgtgcaa cgtcagcatg gcggcactcg acaagttcgt tgcggaacgc atcttcaaca agatcaggca cgccgaaggc gacgaagaga cgttggcgct tctgtgggaa gccgcccgac gcttcggcaa gctcactgag gcgcctgaga agagcggcga acgggcgaac cttgttgcgg agcgcgccga cgccctgaac gcccttgaag agctgtacga agaccgcgcg gcaggcgcgt acgacggacc cgttggcagg aagcacttcc ggaagcaaca ggcagcgctg acgctccggc agcaaggggc ggaagagcgg cttgccgaac ttgaagccgc cgaagccccg aagcttcccc ttgaccaatg gttccccgaa gacgccgacg ctgacccgac cggccctaag tcgtggtggg ggcgcgcgtc agtagacgac aagcgcgtgt tcgtcgggct cttcgtagac aagatcgttg tcacgaagtc gactacgggc agggggcagg gaacgcccat cgagaagcgc gcttcgatca cgtgggcgaa gccgccgacc gacgacgacg aagacgacgc ccaggacggc acggaagacg tagcggcgta gTctagaGCG ATCCTGGCCT AGTCTATAGG AGGTTTTGAA AAGAAAGGAG CAATAATCAT TTTCTTGTTC TATCAAGAGG GTGCTATTGC TCCTTTCTTT TTTTCTTTTT ATTTATTTAC TAGTATTTTA CTTACATAGA CTTTTTTGTT TACATTATAG AAAAAGAAGG AGAGGTTATT TTCTTGCATT TATTCATGAT TGAGTATTCT ATTTTGATTT TGTATTTGTT TAAATTGTGA AATAGAACTT GTTTCTCTTC TTGCTAATGT TACTATATCT TTTTGATTTT TTTTTTCCAA AAAAAAAATC AAATTTTGAC TTCTTCTTAT CTCTTATCTT TGAATATCTC TTATCTTTGA AATAATAATA TCATTGAAAT AAGAAAGAAG AGCTATATTC GAcctgcagg catgcaagct t Seq. ID No. 26. Edited Int gene in plasmid pKO111 (SacI-HindII) gagctcggta cccaaaGCTC CCCCGCCGTC GTTCAATGAG AATGGATAAG AGGCTCGTGG GATTGACGTG AGGGGGCAGG GATGGCTATA TTTCTGGGAG CGAACTCCGG GCGAATACGA AGCGCTTGGA TACAGTTGTA GGGAGGGATC CATGGCTAGC gacacgtacg cgggtgctta cgaccgtcag tcgcgcgagc gcgaAaattc gagcgcagca agcccagcga cacagcgtag cgccaacgaa gacaaggcgg ccgaccttca gcgcgaagtc gagcgcgacg ggggccggtt caggttcgtc gggcatttca gcgaagcgcc gggcacgtcg gcgttcggga cggcggagcg cccggagttc gaacgcatcc tgaacgaatg ccgcgccggg cggctcaaca tgatcattgt ctatgacgtg tcgcgcttct cgcgcctgaa ggtcatggac gcgattccga ttgtctcgga attgctcgcc ctgggcgtga cgattgtttc cactcaggaa ggcgtcttcc ggcagggaaa cgtcatggac ctgattcacc tgattatgcg gctcgacgcg tcgcacaaag aatcttcgct gaagtcggcg aagattctcg acacgaagaa ccttcagcgc gaattgggcg ggtacgtcgg cgggaaggcg ccttacggct tcgagcttgt ttcggagacg aaggagatca cgcgcaacgg ccgaatggtc aatgtcgtca tcaacaagct tgcgcactcg accactcccc ttaccggacc cttcgagttc gagcccgacg taatccggtg gtggtggcgt gagatcaaga cgcacaaaca ccttcccttc aagccgggca gtcaagccgc cattcacccg ggcagcatca cggggctttg taagcgcatg gacgctgacg ccgtgccgac ccggggcgag acgattggga agaagaccgc ttcaagcgcc tgggacccgg caaccgttat gcgaatcctt cgggacccgc gtattgcggg cttcgccgct gaggtgatct acaagaagaa gccggacggc acgccgacca cgaagattga gggttaccgc attcagcgcg acccgatcac gctccggccg gtcgagcttg attgcggacc gatcatcgag cccgctgagt ggtatgagct tcaggcgtgg ttggacggca gggggcgcgg caaggggctt tcccgggggc aagccattct gtccgccatg gacaagctgt actgcgagtg tggcgccgtc atgacttcga agcgcgggga agaatcgatc aaggactctt accgctgccg tcgccggaag gtggtcgacc cgtccgcacc tgggcagcac gaaggcacgt gcaacgtcag catggcggca ctcgacaagt tcgttgcgga acgcatcttc aacaagatca ggcacgccga aggcgacgaa gagacgttgg cgcttctgtg ggaagccgcc cgacgcttcg gcaagctcac tgaggcgcct gagaagagcg gcgaacgggc gaaccttgtt gcggagcgcg ccgacgccct gaacgccctt gaagagctgt acgaagaccg cgcggcaggc gcgtacgacg gacccgttgg caggaagcac ttccggaagc aacaggcagc gctgacgctc cggcagcaag gggcggaaga gcggcttgcc gaacttgaag ccgccgaagc cccgaagctt ccccttgacc aatggttccc cgaagacgcc gacgctgacc cgaccggccc taagtcgtgg tgggggcgcg cgtcagtaga cgacaagcgc gtgttcgtcg ggctcttcgt agacaagatc gttgtcacga agtcgactac gggcaggggg cagggaacgc ccatcgagaa gcgcgcttcg atcacgtggg cgaagccgcc gaccgacgac gacgaagacg acgcccagga cggcacggaa gacgtagcgg cgtagTctag aGAAATTCAA TTAAGGAAAT AAATTAAGGA AATACAAAAA GGGGGGTAGT CATTTGTATA TAACTTTGTA TGACTTTTCT CTTCTATTTT TTTGTATTTC CTCCCTTTCC TTTTCTATTT GTATTTTTTT ATCATTGCTT CCATTGAATT aattcatgca agctt Seq. ID. No. 27 Plastid targeted nuclear int gene in Agrobacterium binary vector pKO117 GAATTCATTT TCACGTGTGG AAGATATGAA TTTTTTTGAG AAACTAGATA AGATTAATGA ATATCGGTGT TTTGGTTTTT TCTTGTGGCC GTCTTTGTTT ATATTGAGAT TTTTCAAATC AGTGCGCAAG ACGTGACGTA AGTATCTGAG CTAGTTTTTA TTTTTCTACT AATTTGGTCG TTTATTTCGG CGTGTAGGAC ATGGCAACCG GGCCTGAATT TCGCGGGTAT TCTGTTTCTA TTCCAACTTT TTCTTGATCC GCAGCCATTA ACGACTTTTG AATAGATACG CTGACACGCC AAGCCTCGCT AGTCAAAAGT GTACCAAACA ACGCTTTACA GCAAGAACGG AATGCGCGTG ACGCTCGCGG TGACGCCATT TCGCCTTTTC AGAAATGGAT AAATAGCCTT GCTTCCTATT ATATCTTCCC AAATTACCAA TACATTACAC TAGCATCTGA ATTTCATAAC CAATCTCGAT ACACCAAATC GATaggatcc AATTCAACCA CAAGAACTAA CAAAGTCAGA AAAATGGCTT CTATGATATC CTCTTCCGCT GTGACAACAG TCAGCCGTGC TTCTAGGGTG CAATCCGCGG CAGTGGCTCC ATTCGGCGGC CTGAAATCCA TGACTGGATT CCCAGTGAAG AAGGTCAACA CTGACATTAC TTCCATTACA AGCAATGGTG GAAGAGTAAA GTGCATGCAG GTGTGGCCTC CAATTGGAAA GAAGAAGTTT GAGACTCTTT CCTATTTGCC ACCATTGACC atggctagcg acacgtacgc gggtgcttac gaccgtcagt cgcgcgagcg cgagaattcg agcgcagcaa gcccagcgac acagcgtagc gccaacgaag acaaggcggc cgaccttcag cgcgaagtcg agcgcgacgg gggccggttc aggttcgtcg ggcatttcag cgaagcgccg ggcacgtcgg cgttcgggac ggcggagcgc ccggagttcg aacgcatcct gaacgaatgc cgcgccgggc ggctcaacat gatcattgtc tatgacgtgt cgcgcttctc gcgcctgaag gtcatggacg cgattccgat tgtctcggaa ttgctcgccc tgggcgtgac gattgtttcc actcaggaag gcgtcttccg gcagggaaac gtcatggacc tgattcacct gattatgcgg ctcgacgcgt cgcacaaaga atcttcgctg aagtcggcga agattctcga cacgaagaac cttcagcgcg aattgggcgg gtacgtcggc gggaaggcgc cttacggctt cgagcttgtt tcggagacga aggagatcac gcgcaacggc cgaatggtca atgtcgtcat caacaagctt gcgcactcga ccactcccct taccggaccc ttcgagttcg agcccgacgt aatccggtgg tggtggcgtg agatcaagac gcacaaacac cttcccttca agccgggcag tcaagccgcc attcacccgg gcagcatcac ggggctttgt aagcgcatgg acgctgacgc cgtgccgacc cggggcgaga cgattgggaa gaagaccgct tcaagcgcct gggacccggc aaccgttatg cgaatccttc gggacccgcg tattgcgggc ttcgccgctg aggtgatcta caagaagaag ccggacggca cgccgaccac gaagattgag ggttaccgca ttcagcgcga cccgatcacg ctccggccgg tcgagcttga ttgcggaccg atcatcgagc ccgctgagtg gtatgagctt caggcgtggt tggacggcag ggggcgcggc aaggggcttt cccgggggca agccattctg tccgccatgg acaagctgta ctgcgagtgt ggcgccgtca tgacttcgaa gcgcggggaa gaatcgatca aggactctta ccgctgccgt cgccggaagg tggtcgaccc gtccgcacct gggcagcacg aaggcacgtg caacgtcagc atggcggcac tcgacaagtt cgttgcggaa cgcatcttca acaagatcag gcacgccgaa ggcgacgaag agacgttggc gcttctgtgg gaagccgccc gacgcttcgg caagctcact gaggcgcctg agaagagcgg cgaacgggcg aaccttgttg cggagcgcgc cgacgccctg aacgcccttg aagagctgta cgaagaccgc gcggcaggcg cgtacgacgg acccgttggc aggaagcact tccggaagca acaggcagcg ctgacgctcc ggcagcaagg ggcggaagag cggcttgccg aacttgaagc cgccgaagcc ccgaagcttc cccttgacca atggttcccc gaagacgccg acgctgaccc gaccggccct aagtcgtggt gggggcgcgc gtcagtagac gacaagcgcg tgttcgtcgg gctcttcgta gacaagatcg ttgtcacgaa gtcgactacg ggcagggggc agggaacgcc catcgagaag cgcgcttcga tcacgtgggc gaagccgccg accgacgacg acgaagacga cgcccaggac ggcacggaag acgtagcggc gtagtctaga gTCGAAGCAG ATCGTTCAAA CATTTGGCAA TAAAGTTTCT TAAGATTGAA TCCTGTTGCC GGTCTTGCGA TGATTATCAT ATAATTTCTG TTGAATTACG TTAAGCATGT AATAATTAAC ATGTAATGCA TGACGTTATT TATGAGATGG GTTTTTATGA TTAGAGTCCC GCAATTATAC ATTTAATACG CGATAGAAAA CAAAATATAG CGCGCAAACT AGGATAAATT ATCGCGCGCG GTGTCATCTA TGTTACTAGA TCGaccTGCAG

While certain of the preferred embodiments of the present invention have been described and specifically exemplified above, it is not intended that the invention be limited to such embodiments. Various modifications may be made thereto without departing from the scope and spirit of the present invention, as set forth in the following claims. 

1. A transgenic plant comprising a phiC31 integrase and a selectable marker gene which are functional and present in plant plastids, said plastids comprising a nucleic acid encoding a heterologous protein of interest, wherein the nucleic acid is flanked by an attL and an attR site.
 2. A method for producing the plant of claim 1, said method comprising the steps of a) providing a recipient plant having within its plastid genome a first att site recognized by phiC31 integrase, said att site being selected from the group consisting of attP and attB; b) introducing a phiC31 integrase into a plant cell obtained from the plant of step a) via a delivery method selected from the group consisting of 1) transformation of the plant nucleus with a plasmid comprising a nucleic acid encoding said integrase operably linked to a nucleic acid encoding a plastid transit sequences, and 2) transformation of the plastids of the plant cell with a nucleic acid encoding said integrase; c) introducing into said plant cell a DNA construct comprising at least one sequence encoding a heterologous protein of interest and a second att site recognized by said integrase, said att site being selected from the group consisting of attP and attB, said second att site being different from said first att site, and a selectable marker gene, wherein said integrase acts on said first and second att sites, thereby catalyzing insertion of said DNA construct into said plastid genome; and d) generating a plant from the plant cell of step c), said plant producing said heterologous protein of interest.
 3. A transgenic plant comprising a) a phiC31 integrase which is functional and present in a plant plastid and b) transformed plastids comprising a nucleic acid encoding a heterologous protein of interest, wherein the nucleic acid is flanked by an attL and an attR site.
 4. A method of producing the plant of claim 3, said method comprising the steps of a) providing a recipient plant having within its plastid genome a first att site recognized by phiC31 integrase, said att site selected from the group consisting of attP and attB; b) introducing a phiC31 integrase into a plant cell obtained from the plant of step a) via a delivery method selected from the group consisting of 1) transformation of the plant nucleus with a plasmid comprising a nucleic acid encoding said integrase operably linked to a nucleic acid encoding a plastid transit sequence, and 2) transformation of the plastids of the plant cell with a nucleic acid encoding said integrase; c) introducing into said plant cell a DNA construct comprising at least one sequence encoding a heterologous protein of interest and a second att site recognized by said integrase, wherein said att site is selected from the group consisting of attP and attB, said second att site being different from said first att site, wherein said integrase acts on said first and second att sites, thereby catalyzing insertion of said DNA construct into said plastid genome; and d) generating a plant from the plant cell of step c), said plant producing said heterologous protein of interest. 